The present invention generally relates to soldering materials and more particularly to self fluxing, toxicity free materials especially suitable for joining of tubing, fittings, and fixtures used in plumbing.
Soldering materials having lead as a base have been proven to be toxic and therefore their use has been banned. Hence, there is a need for non-lead base soldering materials with the same characteristics as easy flow, good wettability and low temperature operation. Joints formed by such materials should also have good corrosion and physical strength characteristics. Non-lead base materials have been used in past to produce high temperature brazing alloys which are not suitable for plumbing or other operations requiring low temperature heating for joining. Moreover, they are expensive, making them unattractive for general purpose use. Other non-lead soldering materials which have been used in the plumbing industry have included other toxic materials such as cadmium and antimony, and are thus likewise unsuitable for joining piping and tubing using to transport drinking water.
The following patents are representative of the approaches which have been taken:
U.S. Pat. No. 4,357,162 relates to a soldering material based on silver (20 to 40%) with copper and tin. The material is stated to be useful in the semiconductor industry but obviously is too expensive for plumbing applications because of its large silver content.
U.S. Pat. Nos. 3,087,813 and 1,103,482 describe soldering materials with varying amounts of silver, tin, copper, and aluminum.
U.S. Pat. No. 4,778,733 provides details of soldering materials based on tin with silver and copper, and without lead or antimony whose toxic nature is noted. These materials are non-fluxing type and fluxing agents, however, are required to be added separately to get better joining properties of this group of materials. The small amounts of silver added, as in my self fluxing composition, are adequate to raise the surface tension so as to avoid spattering during soldering.
U.S. Pat. No. 2,004,372 and U.S. Pat. No. 2,864,733 in which compositions of high zinc content that are suitable for aluminum alloys, are described. In plumbing joints use of such compositions can promote brittleness. Amounts less than 0.5% Zinc are sufficient to ensure wettability of soldering area and produce a joint that is crack free and leakproof.
U.S. Pat. Nos. 4,695,428 and 4,758,407 disclose solder alloys which are primarily tin/antimony based. The latter patent also describes a tin based solder which includes copper, nickel and silver, but not zinc.